Femtosecond to picosecond processes are often considered to be a thermalizing bath that has little effect on longer time scale photocatalytic reactions. In this talk, we will discuss when strong defect or electron-phonon interactions can be the rate limiting step in photocatalytic materials and junctions. Specifically, high harmonic generation is used to create X-ray pulses with attosecond pulse widths and energies covering 10-150 eV. The XUV pulse is combined with a 3-5 femtosecond excitation pulse and an optical delay line to allow for transient absorption measurements. The response of the elemental X-ray edges is separated into electronic and thermal structural components using the Bethe-Salpeter equation. This approach allows for the heat and charge transfer to be measured as a function of an elements in a material. For example, the conversion of photoexcited electrons to polarons is compared between Fe2O3 and CuFe2O4. The time-resolved energy of electrons and holes controls the filling of surface defect states or charge transfer to metal catalysts in ZnTe and ZnTexSe1-x alloys. Finally, hot hole transport is measured between each component of a metal-insulator-semiconductor junction (Ni-TiO2-Si) using the Ni, Ti, and Si X-ray edges.

When femtosecond processes play a determining role in photoelectrochemistry

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ACS Fall 2022

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